This invention relates to change-over switches for an on-load tap changer, and more particularly to improvements in a main arcing roller contact and a current-carrying roller contact useful for a compact design.
FIG. 1 is a sectional view of a conventional two-resistor-type roller contact-type change-over switch for one phase power, hereinafter simply referred to as a change-over switch. FIG. 2 is an explanatory view taken along the line II--II of FIG. 1. This change-over switch comprises a cylindrical insulating housing 1, an arcing mechanism unit 2 for providing an arc interrupting function upon tap changing, a current-carrying mechanism unit 3 for providing a current-carrying function, and a collector mechanism unit 4 providing a current-collecting function during both the tap changing and the current carrying.
An arc interrupting roller contact or arcing roller contact or arcing roller 5 which is a main component of the arcing mechanism unit 2 is made of an arc resisting material and is composed of three members: a main arcing roller 5a and resistant arcing rollers, 5b and 5c, arranged on the left and right, respectively, of the main arcing roller 5a as viewed in FIG. 2. On the central axes of these arcing rollers 5a, 5b, and 5c are disposed a current-carrying bushing or arcing current-carrying bushing 6a for the main arcing roller 5a which is rotatable relative to the main arcing roller 5a as well as resistant current-carrying bushings 6b and 6c for the resistive arcing rollers which are rotatable relative to the resistive arcing rollers 5b and 5c. The arcing rollers 5a, 5b and 5c are supported by arcing roller contact holders or arcing holders 7a, 7b and 7c having a U-shaped cross section and the ends of the arcing current-carrying bushings 6a, 6b and 6c are respectively fixed thereto. The arcing holders 7a, 7b and 7c are mounted on a movable contact drive shaft 8. The movable contact drive shaft 8 is mounted on an insulating drive shaft 9 positioned on the center line of the insulating housing 1, and the movable contact drive shaft 8 is arranged to rotate by the rotation of the insulating drive shaft 9. Coil springs 10a, 10b, 10c are inserted under compression between the arcing holders 7a, 7b, 7c and the movable contact drive shaft 8, and the respective arcing holders 7a, 7b and 7c are always biased in the radial direction by the spring function of the coil springs 10a, 10b, 10c. Therefore, the arcing rollers 5a, 5b and 5c are pressed against the arcing fixed contacts 11A, 11B which are fixed at equal intervals on the inner periphery of the wall of the insulating housing 1 and made of an arc resistive material. Reference numeral 12a designates one of three stoppers for determining the wiping distance upon the separation of the arcing rollers 5a, 5b and 5c; the other two stoppers not being shown in the drawings.
A principle roller contact current-carrying roller contact 13 (hereinafter referred to as a current-carrying roller) which is a main component of the current-carrying mechanism unit 3 is made of an electrically conducting material, and a current-carrying bushing 14 for a current-carrying roller is rotatably mounted on its central axis. The current-carrying roller 13 is supported on the movable contact drive shaft 8 by a current-carrying roller contact holder or current-carrying holder 15 disposed immediately below the main arcing holder 7a with the opposite ends of the current-carrying bushing 14 secured thereto. Similarly to the arcing mechanism unit 2, a coil spring 16 is compressed between the current-carrying holder 15 and the movable contact drive shaft 8, and a stopper 17 is mounted to the current-carrying holder 15, which function in the same manner as described in conjunction with the arcing mechanism unit 2. The current-carrying roller 13 is arranged to cause the current-carrying fixed contacts 18A and 18B fixed, at equal intervals, on the inner periphery of the wall of the insulating housing 1 to be pressed upon by the spring action of the coil spring 16. The current-carrying fixed contacts 18A and 18B are made of an electrically conductive material and are disc shaped, and are centrally positioned immediately below the arcing fixed contacts 11A and 11B.
A current-collecting roller contact of collecting roller 19 which is a main component of the collector mechanism unit 4 is also supported on the movable contact drive shaft 8 by a current-collecting roller contact holder or current-collecting holder 20 disposed immediately below the main arcing holder 7a in a manner similar to the current-carrying mechanism unit 3 through a current-carrying bushing or current-collecting current-carrying bushing 21 for the current-collecting roller. A coil spring 22 and a stopper 23 having a function similar to that of the arcing mechanism unit 2 are provided within the current-collecting mechanism 4. The current-collecting roller 19 is arranged to press the current-collecting fixed contact 24 disposed on the inner peripheral wall of the insulating housing 1 by the spring action of the coil spring 22. The current-collecting fixed contact 24 is secured on the inner peripheral wall of the insulating housing 1 in the circumferential direction.
On the outer peripheral wall of the insulating housing 1, fixed contact terminals or fixed terminals 26 connected to transformer leads 25 extending from the respective taps in correspondence with the arcing fixed contacts 11A and 11B and the current-carrying fixed contacts 18A and 18B. Also, on the outer peripheral wall of the insulating housing 1, current-collecting contact terminals or current-collecting terminals 28 connected to leads 27 from the transformer main winding are provided in correspondence with the current-collecting fixed contacts 24.
As shown in FIG. 2, the main arcing current-carrying bushing 6a and the current-collecting current-carrying bushing 21 are connected by leads 29. Further, the resistant current-carrying bushings 6b and 6c and the current-collecting current-carrying bushing 21 are connected by leads 31 through a current-limiting resistor 30 mounted on the insulating drive shaft 9. The current-carrying bushing 14 and the current-collecting current-carrying bushing 21 are connected by connecting leads 32.
The operation of the above construction will now be described. In the current-carrying (stop) mode, the current flows through a circuit of the transformer leads 25 to the fixed terminal 26 to the current-carrying fixed contact 18A to the current-collecting roller 13 to the bushing 14 to the connecting leads 32 to the current-collecting current-carrying bushing 21 to the current-collecting roller 19 to the current-collecting fixed contact 24 to the current-collecting terminal 28 and to the leads 27. At this time, since the conductivity of the arcing fixed contact 11A is slightly poorer than that of the current-carrying fixed contact 18A, almost no current flows from the fixed terminal 26 to the arcing fixed contact 11A.
During tap changing, the movable contact drive shaft 8 is rotated by a rotational force applied from the insulating drive shaft 9, and the current-carrying roller 13 is released from the current-carrying fixed contact 18A while being rotated. Therefore, the current path to the current-carrying roller 13 is interrupted and the load current flows into the main arcing roller 5a in a condition with almost no arc. Thus, the load current flows through the transformer leads 25 to the fixed terminal 26 to the arcing fixed contact 11A to the main arcing roller 5a to the arcing current-carrying bushing 6a to the leads 29 to the current-collecting current-carrying bushing 21 and successively through roller 19, contact 24 and terminal 28 along the same current path as previously described into the leads 27.
Further, as the movable contact drive shaft 8 rotates, the main arcing roller 5a separates from the arcing fixed contact 11A while interrupting an electric arc, so that the current is transferred to the resistant arcing roller 5b. The current flows through the transformer leads 25 to the fixed terminal 26 to the arcing fixed contact 11A to the resistant arcing roller 5b to the resistant current-carrying bushing 6b to the leads 31 to the current-limiting resistor 30 to the leads 31 to the current-collecting current-carrying bushing 21 to further flow successively through roller 19, contact 24 and terminal 28 into the leads 27 along the same path as above described. Further, as the movable contact drive shaft 8 rotates, after a bridging condition in connection with the resistant arcing rollers 5b and 5c and the arcing fixed contacts 11A and 11B is experienced, the resistant arcing rollers 5B interrupts the arc, whereby the current flows into the resistant arcing roller 5c. Then, the main arcing roller 5a is brought into contact with the arcing fixed contact 11B of the next tap, and the load current path again shifts to the main arcing roller 5a. Finally, the current-carrying roller 13 is brought into contact with the current-carrying fixed contact 18B, thereby completing the tap changing to provide a current-carrying condition.
Since a conventional roller contact type changer-over switch is separated between the arcing mechanism unit 2 and the current-carrying mechanism unit 3 as above described, the volume of the entire apparatus is disadvantageously large. Also, since the arcing mechanism unit 2 and the current-carrying mechanism unit 3 are separately constructed, two sets of parts (two sets of roller contact holders 7a, 15, two sets of current-carrying bushings 6a, 14, two sets of coil springs 10a, 16, etc.) are necessary. Not only does the number of parts become large, but their manufacture and assembly becomes complicated since a part for the arcing mechanism unit 2 is not identical in structure to the corresponding part in the current-carrying mechanism unit 3. The cost of manufacturing and assembly therefore increases.